One of the main criticisms of most theories of personality is that they
have difficulty accounting for the irrational, less predictable patterns
of human thinking and behavior. Psychoanalytic theory, on the
other hand, heads straight for the jugular, the deep, mysterious core of
the human psyche, in search of understanding the psychology of the
human.

In fact, psychoanalytic theory, developed initially by Sigmund Freud
during the latter part of the 1900s and during the early decades of the
21st century, formed the foundation of modern psychology. Much of
the theory and research that came later, even if it disagreed with
psychoanalytic thinking, was nevertheless shaped and influenced by its
perspectives.

In considering personality, the broad, unique contribution of
psychoanalytic theory is the suggestion that much of the explanation for
human behavior, which is often bizarre and seemingly contradictory, lies
largely hidden in the unconscious, and is the result of how a person
negotiates conflicting, deep-rooted desires and instincts. There
is overlap with learning theory in that psychoanalytic theory see the
early years of development as making a critical contribution to the
adult psyche, depending on various psycho-sexual stages are resolved.

Here's an example. Why do humans have addictive behaviors, even
though it seems to have ill long-term effects. Sigmund Freud
explained in "Civilization & Its Discontents":

Life as we find it, is too hard for us: it brings us too
many pains, disappointments and impossible tasks. In order to bear it,
we cannot dispense with palliative measures…There are three such
measures: powerful deflections, which cause us to make light of our
misery; substitute satisfactions, which diminish it; and intoxicating
substances which make us insensitive to it.

Psychoanalytic theory is also closely connected with evolutionary
perspectives on personality. Freud accepted the basic insights of
Darwin's evolutionary theory, particularly with regard to the idea that
humans have evolved with particular instincts which were advantageous to
survival. Freud was a medical practitioner and researcher who
transformed himself into the world's first psychologist. His
evidence was mostly based on case studies of his work with people who
were suffering neuroses of one variety or another.

Freud's theories have come under criticism from many quarters, including
Carl Jung, who was a student and colleague of Freud's, from feminists,
and from researchers who claim that there is a lack of scientific
evidence for Freud's claims. However, there is much in
psychoanalytic theory which continues to be of much use in psychology
and society. Thus, many theorists, researchers, and practitioners
have evolved psychoanalytic theory -- generally refereed to as
neoanalytic theories.